1. From Gene to Protein Central Dogma of Biology: DNA  RNA  Protein

2. Scientists that worked on Protein Synthesis:
Archibald Garrod: pioneered the field of inborn errors of metabolism.
First proposed the relationship between genes and proteins.
George Beadle and Edward Tatum: worked with bread mold Neurospora Crassa
1gene1protein hypothesis
changed to 1gene1polypeptide
some proteins are made from more than one gene

3. Protein Synthesis: overview
Transcription:
synthesis of RNA (mRNA) under the direction of DNA
Translation:
actual synthesis of a polypeptide under the direction of mRNA

4. Compare RNA to DNA: RNA: Ribose 5 C sugar Uracil instead of Thyamine
single stranded
More reactive
3 kinds
m-RNA
t-RNA
r-RNA
DNA:
Deoxyribose 5 C sugar
Thyamine
double stranded helix
More stable

5. Ribosomal (r- RNA): Is the ribosome Site of protein synthesis
Transcribed in the nucleolus
2 sub-units:
smaller 40s sub-unit
larger 60s sub-unit

6. Messenger (m-RNA): Physical link between the gene and the protein
DNA is too large to leave the nucleus
This is what gets translated
m-RNA structure:
5' leader- aids in ribosome binding
Coding region- translates into polypeptide
3' trailer

7. Transfer (t-RNA): Responsible for deseifering the codons
Brings the amino acids together according to sequence on m-RNA
t-RNA structure:
90 nucleotides that pair up causing folding to give its shape
anticodon loop- pairs with the codon of m-RNA

8. The Problem:
How can 4 bases, or combinations there of, code for the 20 different amino acids?
How does the info get from the DNA to the final protein product?
DNA only has 4 variable parts, the 4 different bases.
1. If 1 base coded for 1 amino acid = 41 (4)
2. If 2 bases coded for 1 amino acid = 42 (16)
3. If 3 bases coded for 1 amino acid = 43 ( 64)
20 different amino acids used to make proteins

9. The Triplet Code
Each coding part of DNA (codon) consists of 3 adjacent nucleotides that specify for one of 20 amino acids.
GUU (valine), CUA (leucine), CGU (argenine)
‘U’ (uracil) replaces ‘T’ in RNA
Synonymous codons- are different codons that specify for the same amino acid
Start signal- AUG (methionine)
Stop signal- UAA, UAG, UGA

10. Transcription, I RNA polymerase: Promoter region on DNA:
compliments RNA nucleotides from the DNA code
Promoter region on DNA:
where RNA polymerase attaches site of initiation
Terminator region:
signals the end of transcription
Transcription unit:
stretch of DNA transcribed into RNA

11. Transcription, II Initiation~ Elongation~ Termination~
transcription factors mediate the binding of RNA polymerase to an initiation sequence
Elongation~
RNA polymerase continues adding nucleotides
Termination~
RNA polymerase detaches

12. mRNA modification Capping- methylated cap added to 5' end,
aids in binding to ribosome
Poly A-tail adenines added to 3' tail,
helps transport m-RNA out of the nucleus
Introns- regions that don’t code for protein
Removed by Splicesome to form mature m-RNA (splicing)
Exons- region that expresses protein
Prokaryotic m-RNA have no methylated cap, poly a-tail, or introns ready to go as soon as m-RNA is made

13. Translation, I
mRNA from nucleus is ‘read’ along its codons by tRNA’s anticodons at the ribosome
tRNA has a specific anticodon and amino acid attached

14. Translation, II rRNA site of mRNA codon & tRNA anticodon coupling
P site holds the tRNA carrying the growing polypeptide chain
A site holds the tRNA carrying the next amino acid to be added to the chain
E site discharged tRNA’s

15. Translation, III Initiation~
union of mRNA, tRNA, small ribosomal subunit, followed by large subunit
Elongation~ •codon recognition •peptide bond formation •translocation
Termination~ ‘stop’ codon reaches ‘A’ site
Polyribosomes: translation of mRNA by many ribosomes

16. Mutations: genetic material changes in a cell
Point mutations
Changes in 1 or a few base pairs in a single gene
Mutagens: physical and chemical agents that change DNA
Types of mutations:
Substitutions
Insertions or deletions
Inversion

17. Base-pair substitutions:
Replacement of one nucleotide with another
silent mutations
no effect on protein
missense
to a different amino acid (different protein)
nonsense
to a stop codon and a nonfunctional protein

18. Base-pair insertions or deletions:
Additions or losses of nucleotide pairs
Frameshift mutation - alters the ‘reading frame’ of triplets

19. Inversion: An entire section of DNA is reversed. Example:
May involve only a few bases or large regions of a chromosome containing several genes.
Example:
Original: The fat cat ate the wee rat.
Inversion: The fat tar eew eht eta tac.